Many printing devices are designed to use a long continuous sheet of paper which has been folded to form a series of individual pages. Typically, a folding scheme is used in which inward folds, at which the front sides of adjacent pages face each other, are alternated with outward folds, at which the back sides of adjacent pages face each other. The resulting pattern may be called "Z-fold" because the edges of the pages form a pattern resembling the letter Z.
After pages pass through a printer, it is desirable to stack them neatly to facilitate handling. In the prior art, Z-fold paper was usually allowed to fall into simple trays or wire baskets. One disadvantage of this approach was that the first page of paper often had to be positioned by hand to permit stacking of the following pages. In addition, the edges of the paper had a tendency to "fluff" or remain uncompressed. Another disadvantage was that stacking could be disrupted when a fold landed inward from its proper place at the edge of the stack. This could occur when a page curled as it fell, so that the fold following that page would "dive", that is drop to a position lower than the upper portion of the page. When a diving fold reached the paper stack, it prevented later pages from lying flat.